The Postgraduate Training Program in Medical Imaging (PTPMI) provides recent doctoral graduates with research training in medical imaging, as currently applied to disciplines such as nuclear medicine (PET and SPECT), magnetic resonance imaging (MRI) and computed tomography (CT). The importance of the field of Radiological Sciences has been recognized by the establishment of National Institute of Biomedical Imaging and Bioengineering (NIBIB). And within radiological science, medical imaging research has revolutionized the practice of radiology. Scientists may enter the field of medical imaging research after study of a curriculum that focuses directly on radiological science or after earning a doctoral degree in the physical sciences, mathematics, biophysics, or computer science. The PTPMI will provide trainees a strong background via structured didactic courses and seminars, enabling graduates to critically evaluate the field and formulate their own research ideas. Trainees will participate in leading-edge research, with the opportunity to interact with a world-class faculty in a setting that combines the resources of the Harvard Medical School (HMS), and the Harvard-affiliated Teaching Hospitals. The rationale for this program is based on several factors: 1) the growing need for basic scientists with training in radiological science (PET, MR, CT and optical) including structural, functional, and molecular imaging; 2) the availability of outstanding research programs that provide exciting opportunities for trainees; 3) the availability of modern well-equipped facilities and prototypes imaging systems; 4) an unusually strong group of mentors and, in addition, a faculty who provide additional expertise and extend the range of contacts available to trainees; and 5) long-standing, diverse collaborations, both within the Massachusetts General Hospital (MGH) as well as the Harvard Joint Program in Nuclear Medicine, Harvard Medical School (HMS), other HMS-affiliated hospitals, Harvard University, and Massachusetts Institute of Technology (MIT).